Art of producing musical sounds



Aug. 9, 1938.- G. SMILEY v Re. 20,825

ART OF PRODUCING MUSICAL SOUNDS ELECTRICALLY original Filed Dec. 4,19332 sheets-sheet 1 v /l MCG 4X lip l Il @V ll l I 3 G P y @L VD f Q f l 91 EC 5. Eb i 2 5 wg-wm ?zg 2 //Ocz I2 Y ff/"6H [o U u; f

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ART OF PRODUCING MUSICAL SOUNDS ELECTRICALLY Original Filed Dec. 4. 19532 Sheets-Sheet 2 :e V 6,6 /4 P In Vemor' x//ber/ 5ml/ey "M Reuued Aug.9, 1938 Re. :wsA

OFFICE;4J 'y UI'BICALL ABT F PBODUCING MUSICAL SOUNDS Gilbert Smiley,Bingham, Mal., asaignor, by y mesne lllllmlltl. to Hammond InstrumentCompany; Chicago, I ll., a corporation of Dela- Original No. 2.0,892,dated April 7, 1936, Serial No. 700,837. December reissue 4, 1933.'Application for March 28, 193g No. 198,616

My presentinvention has for.F its object toB produce musical soundselectrically. A more speciilc objectbf my invention is to provide acircuit arrangement for producing an `outputwave which possesses theharmonics,- required under certain conditions, to render a given notemusically desirable or pleasing to the ear.

\ Still another object contemplated is the pro- `Ivision of means foradding to a more or less lo-kpure sinusoidal wave of given frequency, asde- `rived from an appropriate oscillator or appropriate oscillators,one or more additional harmonics of the fundamental of said wave at aproperV amplitude, or for the reinforcement of v harmonics alreadypresent but of insufllcient amplitude, by the use of a vacuum tuberepeater from the output of which the resultant wave form may beampliiled and reproduced by a loud speaker.

To these and other ends my invention comprises further 'improvements allof which will be more iully set forth in theeiollowing specilicatlon andthenovel 'features pointed out in the accompanying claims.

In the drawings:

Fig. 1 is a diagrammatic illustration of a vacuum tube'circuit forrepeating audible frequency The input circuit, across which the incomingoscillations are impressed, comprises the conductors i and 2, the formerleading tlirough a blocking condenser Cg to one end of a voltage- 45divider-3 the slider 3a of which is connected by a conductor 4 to thegrid G, and the latter leading directly to the cathode K.v The other endof the divider l is connected to the cathode by a conductor 5 in which abiasing source of 50 potential Ec for the grid is provided. The outputcircuit comprises the plate and cathode leads I and 1, which may beconnected toan amplier I in turn feeding into a loud speaker l, as willbe understood. The plate lead I has`a blocking 65. condenser Cpconnected therein. The platecathode circuit omprisesthe source Eb forsupplying the operating potential tothe plate P and the resistance Rthrough which said potential is supplied and which serves as a couplingresistance' inthe output circuit. The condensers 5 C g' and Cp preventthe operating D. C. potentials from being transmitted through the inputand output terminals to the instrumentalities connected thereto.

Any convenient source or sources of oscillal0 tions feed into the inputconductors i and I. In Fig. 1 I have shown a single source S connectedto these conductors. In my develop-v ment of musical instruments for theplaying of chords, however, I employ a series of independl5 ent ordependently relatedk sources of oscillations, such as va'cuum tubeoscillatory circuits, tuned to the various lfrequencies called for bythe various keys of the keyboard. Thus, several or all of theseoscillatory circuits may be adapted to feed into the repeater circuitshown in Fig. 1, each oscillatory circuit so connected be-v v ingarranged to supply a proper proportion of its' output when the keyassociated with the frequency or notewhich it produces is struck ordepressed. If desired, a separate repeater .circuit may nevertheless beprovided for each of the sources, each repeater circuit receiving theproper' intensity of output from its associated source when the latter'skey is depressed. 30

The keyboard may be of conventional construction used in electricalmusical instruments such, for example, as that diagrammaticallyillustrated in my Patent No. 2,083,246, dated June 8, 1937, or as shownin the patent to Cahill No. 1,213,804. dated January 23, 1917. For theproduction of single notes, the repeater circuit vof Fig. 1 may beassociated with a single oscillator, the frequency of Iwhich iscontrollable by suitable means. cooperating with the keyboard.

I have foundin practice that inmany of the types of oscillators orgenerators of audible frequency voltage waves, the wave form produced istoo pure, i. e., too close to a sinusoidal wave to create variousdesirable musical effects. In 4,5 other words, such a wave form does notreproduce a musical note acceptable for many purposes, as it is lackingin timbre.

My invention contemplates broadly introducing an oscillatory w'ave of vapure or insuillciently 50 `impure form into a repeater circuit and thereintroducing the necessary harmonics to produce 'what is known in amusical sense as overtones,

the final output from the repeater being a wave., form which, by propercontrol, is caused to renlieranotesimilaroridenticaltotbataomidedvbyaninstrmnentitmaybedeai/redtoaimulate. or, moreover. to creatediscrete tonal eilects. not necessarily imitative of existinginstruments. but none the less pleasing and desirable. In general thisis accomplished by the introduction in the repeater circuit ofsuchcontroiling elements that the harmonic content lof the output y wavemay be widely varied to permit desired and desirable tonal eiIects to beattained.y

'lhe object desired may be accomplished by controlling both the gridbias of the repeater tube V and theamplitude of the input wave andtaking advantageof the repeater tube characteris tics. The grid bias maybe controlled by proper adjustment of the potential of the supply Ec,and the amplitude of the input wave may be controlled by properadjustment of the slider 3o on the voltage-divider t.

20.? Ihe curve il shown in Figs. 2 to 5 inclusiv mimmo the plate-currentcharacteristic of a.

repeater tube V such as I may employ in accordance with my invention. InFig. 2 this tube is operated as a linear repeater, in which case theoutput wave. which corresponds to the plate current wave Il. is anamplified facsimile of the grid potential wave il produced by theiniluence of the incoming fluctuating wave. In operating the repeatercircuit in this instance the grid bias potential is selected, asindicated by the axis Ecl. to fall at about the center of the straightportion of the plate current characteristic curve II. This bias is suchthat equal grid potential changes. within certain limits. produce equalplate current changes about the steady plate current. indicated by theaxis Ipi. resulting under the steady bias conditions. Thus, practicallyno distortion results when alternating potential of amplitude Al isapplied to the grid G. causing an output wave of double amplitudeBbetween crests to be es tablished about the plate axis Ipl.

A comparison of the sure just described with Fig. 3 shows how harmonicsof appreciable magnitude may be introduced in the output wave byincreasing the grid operating potential in a negative direction. Theamplitude of the grid potential wave is at the same time slightlyincreased to the value A2, which is done to maintain the desired doubleamplitude B of the output wave in the plate circuit. As seen. the inputwave il is established along the new axis Ecl. which results a inshifting the plate axis to Ip along which the output wave Il iscorrespondingly distorted from its former approximately sinusoidal formshown in Fig. 2.

InFig.4Ihaveillustratedthebiasofthegrid of the repeater tube adjusted toplace the input axis at the cut-oi! point Ecl of the plate currentcharacteristic curve il. In this case the amplitude of the input voltagemust be considerably' increased. as its new value AI indicates. in orderto maintain the output corresponding to a fluctuating flow of current inthe plate circuit at the same amplitude as before. As observed, theoutput wave it established along the new axis Ip) as a result of thegrid potential iiuctuations Il is in this instance -denitely distorted.its wave form introducing such harmonics as to adapt it for certainmusical Pig. 5 shows a furtherdiustment of the grid bias to a point Eclbeyond the cut-ofi' point of the tube and it is seen that, in order tocontinue the output at the'same double amplitude B. itisnecessarytostillfurtherincreasetheamplitude ofthe input wave, as shownby M. The input wave iaindioa'ted by I1 and. as observed, the

'output wave il estabnsnednongtne mastuigreater degree from thatsupplied to the repeater input.V

platecurrentpassingonlyduringthe crestso! the more positive half cyclesoi the input wave.

Prom the above description it is apparent that the present inventionprovides the distinct ad` vantage that various musical eects as totimbre or tone quality of the notes produced may be obtained by properadjustment oi the operating 1 parameters of the tube V. Satisfactorycontrol oi the resultant wave form supplied to the ampliiler l and loudspeaker t is in this manner effected without the use o! variable nltermeans otherwise necsary for such control. were a sufficiency ofharmonics in the first place available. In practice, the operatingparameters of the tube may be made variable. either continuously or inpredetermined steps, between condition: Afor maximum linearity orminimum distortion and conditions for any selected maximum ofdistortion.r

In either case, the amplitude oi the input wave and the operatingpotential at the grid may be adjustable simultaneously to maintain theirproper relationship for Van essentially constant apparent volume output.An `arrangement for such simultaneous adjustment is shown schematicallyin Fig. 6. A voltage-divider Il is connected across the source Ec andits slider 20o is operated conjointly with the slider la of the dividerl, as by a common handle 2|. If desired. the ampliiler 8 may includesuitable illter means for the elimination of undesirable orover-amplitude harmonics or' their attenuation to negligible ordesirable amplitude in the manner known in the art. It is understoodvthat the operating parameters of the tube may be selected to producedesired harmonics of a desired amplitude and thereafter made permanent.In this instance a nlter means is provided for controlling the harmoniccontent.

It is understood that. if desired. such values oi' operating potentialEc may be provided at the' gridofthetubevastocausetheinputpotentialchanges to swing through the upper portions Ila (Fis. 2) oi' thecharacteristic curve IU. The distorting eilects which are obtained inthis manner are similar to those which have been described. In thisinstance the more the grid supply-potential is increased in a positivedirection. the richer is the harmonic content of the output wave. It is.of course, understood that the more the grid supply-potential isincreased in a positive direction. the greater the amplitude to whichthe input wave should be adjusted to maintain the intensity ofthe outputwave substantially constant. However. this distortion is much the sameas will be realised by operation on the low plate current-end oi thecurve it. and has the disadvantage that,.in some instances. the grid ofthe tube V will draw current placing an appreciable load on theoscillatory source. which may, in some'instances. destroy stability offundamental frequency. Further, in drawing current. the grid -mayintroduce certain.y high order harmonics which are usually musicallyundesirable. For these it is generally preferableV to operate the gridin the more negative region, though the invention comprises allpossibilities of deliberate distortion in repeater circuits.l

Although the invention is illustrated in the drawings and describedherein in connection withasinglerepeafertube.itisunderstood thatcircuits involving a plurality oi repeater 7l men-muy disposed in absck-to-bwx circuit ao,sas

when. en or sich is operates m a manner u muy constant. masupply-potential varying bed, may be used to produce other demeanseiIecting harmonic introduction between descri sirable musical effects.lior example, a non-linearly operated repeater tubes may be used in apush-pull" arrangement, i. e., symconnection. Assuming the requiredbalance between such tubes, no even harmonics will be found to exist inthe output wave other than those already in the input wave.

I claim: v

i. In a musical instrumelt, the combination with means for producingelectrical oscillations ofaudible frequency, of a harmonic introducingthermionlc tube repeater Acircuit to which said oscillations aresupplied, said repeater circuit comprising means for varying its gridoperating potential to vary the harmonic ntent of its outputoscillations, said repeater circuit also comprising means for varyingthe lamplitude of the input oscillations at its grid to maintain theintensity of its output oscillations substantially constant.

2. In a musical instrument, the combination with means for producing anaudible frequency electrical wave of substantially pure sinusoidal form,of a wave distorting thermionic tube repeater circuit to which said waveis supplied, said repeater circuit comprising means for varying its gridsupply-potential to vary the form of its output wave, said repeatercircuit also comprising means for varying the amplitude of the inputwave at its grid to maintain the intensity of its output wavesubstantially constant.

3. In a musical instrument, the combination with means for producingelectrical oscillations of audible frequency, of a harmonic introducingthermionic tube repeater circuit to which said oscillations aresupplied, said repeater circuit comprising. means for varying its gridsupplypotential to vary the harmonic content of its output oscillations.said repeater circuit also comprising means for varying the amplitude ofthe input oscillations at its grid to maintain the intensity of itsoutput oscillations substantially constant, said supply-potentialvarying means in one of its positions of adjustment eifecting a biasvalue at cut-off or beyond causing maximum introduction of harmonics.

4. In a musical instrument, the combination with means ior producing anaudible frequency form, of a wave distorting thermionic tube repeatercircuit to which said wave is supplied, said repeater circuit comprisingmeans for varying its grid supply-potential to vary the form of itsoutput wave, said repeater circuit also comprising means for varying theamplitude of tensity of its output wave substantially constant,

,said supply-potential varying means in one of its positionsof-adiustment effecting a bias value at cut-oil or beyond. causingmaximum wave distortion.

5. In a musical instrument, the combination with means for producingelectrical oscillations of audible frequency, oi a harmonic introducingthermionic tube repeater circuit to which said oscillations aresupplied, said repeater circuit comprising means for varying its gridsupplypotential to vary the harmonic content of its comprising meansfor. varying the amplitude of the input oscillations at its grid tomaintain the intensity oi its output oscillations substanelectrical waveof substantially pure sinusoidal the input wave at its grid to maintainthe in output oscillations, said repeater circuit also (conditions forsubstantial absence of harmonic introduction and conditions for apredetermined 'l maximum of harmonic introduction.

6. In a instrument, the vcombination with means for producing any.audible frequency electrical wave of substantially pure sinusoidalform, of a wave distorting thermionic tube repeater circuit to whichsaid wave is supplied, said repeater circuit comprising means forvarying its grid supply-potential to vary the form of its output wave,said repeater circuit also comprising means for varying the amplitude ofthe input wave at itsgrld to maintainthe inltensity of its output wavesubstantially constant, said supply-potential varying means effectingwave distortion between conditions for substantial absence of wavedistortion and conditions for a predetermined maximum wave distortion.v

7. In a musical instrument, the combination with means for producingelectrical oscillations of audible frequency, of a harmonic introducing.

thermionic tube repeater circuit to which said oscillations aresupplied, said repeater circuit comprising means for varying its gridoperating potential to vary the harmonic content of itsoutputoscillations, said `repeater circuit also comprisiri meanssimultaneously operated with said operating potential varying means forvarying the amplitude of the input oscillations at its grid to inaintaintheintensity of its output oscillations substantially constant.

gln a musical instrument, the combination with means for producing anaudible frequency electrical wave of substantially pure sinusoidal form,of a wave distorting thermionic tube repeater circuit to which said waveis supplied, said repeater circuit comprising means for varying its gridsupply-potential to vary thel form ofits output wave, said thermioniccircuit also comprising means simultaneously operated with saidsupply-potential varying means for varying the amplitude of the `inputwave at its grid to maintain the intensity of its output wavesubstantially constant. g

9. In a musical instrument, the combination with means for producingelectrical oscillations of audible frequency, of a harmonic introducingtherrnionic tube repeater circuit to which said oscillations aresupplied, said repeater-circuit comprising an adjustable source ofgrid-supply potential for varying the harmonic content of its outputoscillations, and a voltage-divider for varying the amplitude of theinput oscillations at its grid to maintain the intensity of its outputoscillations substantially constant.

10. In a. musical instrument, the combination with means for producingelectrical oscillations of audible frequency, of a. harmonic introducingthermionictube repeater circuit to which said oscillations are supplied,said repeater circuit comprising an adjustable source of grid-supplypotential for varying the harmonic content of its output oscillationsand a voltage-divider for varying the amplitude of the inputoscillations at its grid to maintain the intensity of its outputoscillations substantially constant, said voltagedivider and saidadjustable source being operated simultaneously.

ll. For use in an electrical musical instrument having a keyboardconsisting of a plurality of keys adapted for'playing chords, a circuitcombination comprising, a series of sources of electrical 75hmndtothendomplicheseslledtor lctthodatothepoint'hetelwrdtblepll'-Momydllrlnlbrldinternbof u. mhmmexmwmuedmnmmenc having s keyboardconsisting of s plurality of

